COVID-19 diagnostic testing has now been available for several weeks to test for active COVID-19 infections. You might now be hearing about COVID antibody tests, also called serology tests. Results from this blood test might help indicate who has, and how many people have had COVID-19 in the past.
What are antibodies?
In response to an infection, your immune system creates two special proteins called IgM and IgG antibodies. IgM appears first, and then IgG. Usually, the IgG antibodies can still be found in the blood and other tissues for a long time after the infection. The next time the body is exposed to that same infection, the IgG antibodies will try to fight off that infection but there are minimum antibody levels typically needed for true immunity.
The COVID-19 IgG antibodies usually develop 1-3 weeks after infection (the timeline seems to vary depending on whether the person showed symptoms of COVID-19 or not). The COVID-19 antibody test takes a sample of your blood and looks for IgG antibodies specific to COVID-19. The blood test will identify if you have IgG antibodies and should also measure the amount of antibodies. Results are usually available within 72 hours.
What do the testing results mean?
At the moment, antibody blood testing alone should not be used to confirm an active, positive COVID-19 infection; for that you will still need a COVID-19 diagnostic swab test. According to the CDC, a positive antibody blood test result shows you have antibodies that likely resulted from COVID-19. If you have a negative antibody blood test result, it could mean a number of things: you did not have a previous COVID-19 infection, or you have a current infection and the IgG antibodies have not appeared yet in your blood (which is why the NYS DOH recommends waiting at least 21 days before testing for antibodies if you were previously diagnosed with COVID-19 from the nasopharyngeal swab test).
It’s not yet clear how much immunity from reinfection the COVID-19 antibodies provide and for how long, but the COVID-19 antibodies are expected to generally behave the same way antibodies have acted with other types of coronaviruses and offer some level of protection. Over the upcoming weeks, we expect to hear more complete information about antibody effectiveness from emerging studies on COVID-19 immunity. Check with the CDC or local Departments of Health for the latest on immunity research and current recommendations around antibody testing.
How can you get antibody testing?
Just as with COVID-19 diagnostic testing, antibody testing is covered by the Families First Coronavirus Response Act and there is no cost-sharing for the provider visit or the test.
Many commercial antibody tests are appearing on the market, but they could vary in their accuracy. The information on testing is still developing. We’ll continue to share more insights as we learn more.